A scan tool is a great tool to have, since sooner or later, the check engine light will come on in your vehicle (inevitable as death and taxes).
But although a scan tool is now a must-have tool, there are many big misconceptions about what it can and can not do.
In this article, I'll try to dispel some of the most common misconceptions that will help you to see your scan tool in a new light (and be able to make effective use of it).
Contents of this tutorial:
The Bare Essentials
All modern fuel injected vehicles have computers controlling the injection of fuel and the creation of spark to start and keep the engine running. Not only that, if the vehicle is equipped with an automatic transmission, it will also be controlled by the same computer or a dedicated transmission computer.
Eventually, the input sensors that help these computers make decisions and keep the vehicle running smoothly and from polluting too much will fail and need to be replaced.
When this happens, the very first symptoms you'll see is the check engine light (CEL) lighting up on your instrument cluster. Why? Well, because all modern fuel injected gasoline engine vehicles have On Board Diagnostics (OBD) integrated in their computers.
It's the job of the OBD system to monitor for failures since a failure in any of the input sensors and output devices will mean that your vehicle will pollute more than it should and of course, your vehicle will not run right.
The tool that's used to interface with your vehicle's On Board Diagnostic system is the scan tool. And so, in a nutshell, to diagnose this check engine light and the problem causing the it light up, you'll need a scan tool.
Taking into consideration that the scan tool will help you to diagnose a check engine light problem, you can conclude that the scan tool is a very important tool to own and to know how to use.
But, there are some very serious misconceptions about what the scan tool can do. Two of the most common are:
Misconception #1: The scan tool will tell you exactly what to replace. This myth costs consumers a ton of money every year. How? Because the vehicle owner (and even the professional auto mechanics) assume that if the diagnostic trouble code is accusing so and so part, it must be bad and should be replaced no questions asked. Sadly, this is not true.
In my long experience working on cars (and of course this is just my opinion), a scan tool will only tell you exactly what's wrong about 20% of the time. Now, don't let this frustrate you, I'll explain this issue some more in the next subheading.
Misconception #2: That connecting a scan tool and reading the diagnostic trouble codes is a diagnostic. This myth also leads to a great big money pit.
Check Engine Light Came Back!
The biggest reason why the check engine light comes back (or never goes away) after replacing the parts the code or codes indicated as being bad, is that those parts were not independently verified apart from the scan tool.
No, I don't mean that the part had to be physically removed and taken to the factory dealer or an auto repair shop to get independently tested. What I mean is that after reading the trouble codes, no tests were performed on the said parts to make sure they were truly fried.
Yes, it is possible to make sure that what the scan tool is telling you is fried, and lighting up the check engine light, is really bad. Let's turn the page and find out more about this.